Flow-priority optimization of additively manufactured variable-TPMS lattice heat exchanger based on macroscopic analysis

Heat exchangers incorporating triply periodic minimal surface (TPMS) lattice structures have attracted considerable research interest because they promote uniform flow distribution, disrupt boundary layers, and improve convective heat transfer performance. However, from the perspective of forming a macroscopic flow pattern optimized for heat exchange efficiency, a uniform lattice is not necessarily the optimal configuration. This study presented a macroscopic modeling approach for a two-fluid heat exchanger equipped with a TPMS Primitive lattice. Macroscopic flow analysis was conducted based on the Darcy–Forchheimer theory. Under the assumption that heat is transferred solely at the interface between the fluid and TPMS walls, a macroscopic heat transfer model was developed using a volumetric heat-transfer coefficient, which serves as an artificial property characterizing the unit-volume heat transfer capability. To effectively regulate the relative dominance of the hot and cold flows and the channel widths within the heat exchanger, we adopted the isosurface threshold of the TPMS Primitive lattice as the design variable and constructed an optimization scheme for the lattice distribution using a previously described macroscopic model. Optimization was subsequently performed for a planar heat exchanger, where the hot and cold fluids followed U-shaped flow trajectories. The optimal solution was verified, and its validity was examined through detailed geometric analysis and experiments conducted using metal-based laser powder bed fusion. The optimal solution derived from the macroscopic model demonstrated a clear performance improvement over a uniform lattice, with an average enhancement of 24.2% in the detailed-geometry simulations and 23.3% in the experimental results.